1. Field of the Invention
The present invention is concerned with new polymers, new anti-reflective compositions containing such polymers and methods of using these new anti-reflective compositions to manufacture microelectronic devices. These compositions include a polymer formed from a starting polymer (e.g., epoxy cresol novolac resins) grafted with a chromophore (e.g., trimellitic anhydride, 4-hydroxybenzoic acid).
2. Description of the Prior Art
Integrated circuit manufacturers are consistently seeking to maximize substrate wafer sizes and minimize device feature dimensions in order to improve yield, reduce unit case, and increase on-chip computing power. Device feature sizes on silicon or other chips are now submicron in size with the advent of advanced deep ultraviolet (DUV) microlithographic processes.
However, a frequent problem encountered by photoresists during the manufacturing of semiconductor devices is that activating radiation is reflected back into the photoresist by the substrate on which it is supported. Such reflectivity tends to cause blurred patterns which degrade the resolution of the photoresist. Degradation of the image in the processed photoresist is particularly problematic when the substrate is non-planar and/or highly reflective. One approach to address this problem is the use or an anti-reflective coating applied to the substrate beneath the photoresist layer.
Compositions which have high optical density at the typical exposure wavelengths have been used for some time to form these anti-reflective layers. The anti-reflective coating compositions typically consist of an organic polymer which provides coating properties and a dye for absorbing light. The dye is either blended into the composition or chemically bonded to the polymer. Thermosetting anti-reflective coatings contain a crosslinking agent in addition to the polymer and dye. Crosslinking is initiated thermally, and this is typically accomplished by an acid catalyst present in the composition.
Typical crosslinking agents include melamines and benzoguanamines. These types of crosslinkers typically impart basicity to the anti-reflective coating formulation, thus resulting in footing of the photoresist profile. This footing profile is not desirable as it can be transferred to the substrate in pattern transfer plasma etch processes. This can lead to device failures. Furthermore, the use of these types of crosslinking agents can affect how the composition planarizes over topography. Most traditional crosslinking agents result in shrinkage of the anti-reflective coating film upon baking, resulting in voids within the via holes, insufficient coverage on top of the via holes, and/or large thickness variations between isolated and dense vias. There is a need for an anti-reflective coating composition that avoids these problems.